This invention relates generally to apparatus for pumping fluids and more particularly, to an impeller for a pump which is suitable for use in the pumping of frothy fluids such as flotation concentrate. An example of such frothy fluid may typically include a mixture of water, air, and mineral particles which can be generated by the flotation of minerals in mining processing plants. It will be appreciated from the following description however that the invention could be suitable for use in other applications. For example, the pump may be suitable for use with viscous slurries.
Mineral processing plants often utilise a process known as flotation to separate the required mineral from the waste rock. This is achieved in a flotation tank or cell in which the slurry is placed and fine air bubbles and reagents are added. The tank is then agitated and the resulting froth which rises to the top of the flotation cell has the fine particles of the required mineral adhering to the froth bubbles. Collection of the froth then provides a means of collecting the required mineral extracted by the process.
The froth from the flotation process contains the required mineral and normally must be pumped to the next processing stage. The different types of froth produced depend a lot on the particles sizes being floated, the type and quantity of reagents and the quantity and size of the air bubbles. The froth process is continuous but at the current time there was no commercial equipment that can reduce the air content of the froth and it is not practical to leave it until the air separates by itself before pumping the froth.
To achieve good recovery results, requires that the mineral be ground to very fine sizes (in some cases less than 10 micron). Also to achieve good mineral recovery the reagents used need to be controlled but quite often this combined with the amount of bubbles necessary to make the process efficient results in a very stable and tenacious froth. These tenacious froths when left in a container would typically take 12 to 24 hours to reduce to the water and solid state only, ie. the bubbles would be extremely slow to disperse.
Pumps for use for pumping froth currently are in the form of vertical and/or horizontally disposed pumps. Vertical pumps are arranged so that the pump inlet is disposed generally vertically and horizontal pumps are arranged with the pump inlet disposed generally horizontally. Vertical froth pumps have been demonstrated to pump very tenacious froth but are quite often physically large and really must be considered in the initial design of a mineral plant, Horizontal pumps on the other hand have been used for froth pumping but are not always successful with tenacious froths. Horizontal pumps have traditionally been deliberately oversized in froth applications. A larger pump means that they can be inefficient with the resultant low flow and high air entrainment due to the froth in a large pump. Mechanical failures can become a problem with unsteady pumping. Froth is full of air but being very small bubble sizes has less effect than the same quantity of air in the form of large bubbles. However, there is a point at which a pumps tolerance to froth will drop due to the effects of the air. The air tolerance of a pump is also related to the net positive suction (NPSH) characteristic; that is, the lower the net pressure available at the intake to the pump the more likely it is that the performance will become effected.
It is an object of the present invention to provide an improved impeller which is suitable for use in froth pumps and improves the performance thereof.
According to one aspect of the present invention there is provided an impeller suitable for use in a centrifugal pump, the pump including a pump chamber and a pump inlet, the impeller including a main body portion which includes a plurality of primary pumping blades or vanes and one or more flow inducing blades or vanes which project from the main body portion of the impeller.
According to another aspect of the present invention there is provided a centrifugal pump including a pump chamber and a pump inlet, and an impeller including a main body portion which includes a plurality of primary pumping blades or vanes and one or more flow inducing generating blades or vanes which project from the main body portion of the impeller, the main body portion of the impeller being within the pump chamber and the or each flow inducing blade extending into the pump inlet, the impeller being mounted for rotation about a central rotation axis and the pump inlet being in the region of the rotation.
The arrangement is such that when in an installed position in the pump, the main body portion of the impeller is disposed within the pump chamber and the or each flow inducing blade extends into the pump inlet. The impeller is mounted for rotation about a central rotation axis and the pump inlet is disposed in the region of the rotation axis. The fluid is then pumped by the pumping vanes and exits therefrom at the periphery of the impeller. The, arrangement is such that the flow of fluid into pump chamber has combined axial and radial flow components.
In one form the main body portion of the impeller includes a shroud on one side of the primary pumping blades, the shroud being remote from the pump inlet when in the installed position. In this particular embodiment, the pumping blades project from the shroud and have a free edge which is adjacent to the pump inlet side of the pumping chamber when in the installed position. Preferably, the or each flow inducing blade is secured to the free edge of one or more of the pumping blades and when installed projects into the inlet. Preferably, each pumping blade has a flow inducing blade associated therewith.
In another form of the invention, the main body includes two spaced apart shrouds with the pumping blades therebetween. In this embodiment, the or each flow inducing blade projects from the shroud adjacent the pump inlet side of the pumping chamber and extends into the inlet.
Preferably, the or each flow inducing blade has an edge which is secured to or integral with a section of the free edge of a pumping blade and extends outwardly therefrom with a face which extends in a generally partially spiral section.
The shape of the flow inducing blades and their position when in the installed position provides additional rotation to the froth before it enters the pump and at the same time provide a better and smoother inlet to the main impeller passageway for the froth. The effect of the flow inducing blades also lowers the net positive head limit requirement that is needed for the pump to perform correctly with tenacious froths for example.
Tenacious froths generally have a high air content so it is difficult to exert any type of force or pressure force to the froth as the forces are not transmitted through the balk of the froth. Hence, the froth will not easily enter the intake of the pump impeller. As the pump impeller adds energy to the fluid or froth it is pumping, it can be seen that it is a necessary requirement to allow the froth to enter the impeller by the easiest means possible. The present invention as well as reducing the inlet NPSH requirements allows the blades or vanes to extend into the pump intake and provides a very much larger improved entry to the impeller; that is less constriction and loss at the impeller entry. When the impeller is rotating the vanes would in practice xe2x80x9cpeel offxe2x80x9d or xe2x80x9cscoop upxe2x80x9d the tenacious froth. By this action the froth will be more easily drawn in to the impeller for pumping.
The invention could normally be applied to any existing pump design but in particular is suitable for horizontal slurry pumps and slurry pumps with an inlet that is larger than is normally required. It could also be applied more easily to open impellers. That is impellers which do not have a front shroud however, as has been described there is nothing preventing the invention being applied to standard pumps or to closed impellers.
Furthermore, the impeller of the invention could be suitable for use to pump any difficult slurry or fluid such as high density visco muds and is therefore not specifically limited to the pumping of froths.